Treatment of formamide



Nov. 7, 1933- P. J. CARLISLE 1,934,485

TREATMENT OF FORMAMIDE Filed 001.. 4, 1929 Z INVENTOR W ATTORN EY Patented Nov. 7, 1933 UNITED STATES PATENT orrics TREATMENT OF FORMAIVIIDE Delaware Application October 4, 1929. Serial No. 397,254

9 Claims.

This invention relates to a method for the vaporization of liquid formamide and a means therefor.

Formamide is a liquid which boils at about -200 C. under a pressure of one atmosphere. When heated ordinarily in the absence of specific catalysts or special precautions, it decomposes to' form mainly carbon monoxide and ammonia. This decomposition increases with the tempera- 10 ture and when the liquid is boiled under a pressure of one atmospherethe rateof decomposition is around 0.5% to 1.0% per minute. The same decomposition occurs in the vapor phase,

but at a considerably slower rate. However,

there is appreciable decomposition of the vapor above 200 C. and especially above 300 C.

This decomposition of heated formamide is a disadvantage when it is desired to use formamide .,vapor in a chemicalprocess, for instance, the

manufacture of hydrocyanic acid.

In order to vaporize formamide with decomposition reduced to the minimum, the liquid must'be brought quickly from a lower temperature, such as room temperature to the vaporization temperature, and vaporization must then occur practically instantaneously. The vapor must not be highly super-heated, preferably not above 300 C. and must be removed to the point .of use in the shortest time possible.

39 It has been proposed to vaporize liquid formamide by allowing it to run onto a heated nonmetallic surface in a relatively thin film at such a rate that there is substantially no accumulation of liquid on the hot surface. While this method is much superior to an ordinary distillation or boiling operation, it allows some decomposition to occur. It also has the disadvantages consequent to the use of a non-metallic construction, namely poorer heat conductivity,

40 greater fragility and higher cost than metal construction. It has been considered impracticable to construct the vaporizer previously proposed of metal because of the possible corrosive action of .hot liquid formamide on metals, and because of possible undesirable catalytic effects of the metals at elevated temperatures.

The objectof this invention is to provide a means whereby formamide may be vaporized in a device constructed of metal.

on a heated metal surface with less decomposition than on a non-metallic surface if conditions are such that vaporization occurs practicallyinstantaneously and the formamide vapor is not superheated to above 300 C. Further- I have found that formamide may be vaporized,

more under these conditions there is no appreciable corrosion of the metal.

The decrease in decomposition by the use of a metal vaporizing surface is probably due to the higher heat conductivity of the metal which allows more formamide to be vaporized in unit time per unit area of heated surface, thus making it possible to maintain the liquid and vapor in contact with the heated surface for a shorter time than when vaporization is carried out on a nonmetallic surface. The absence of corrosion of the metal vaporizing surface is probably due to the small concentrations of the products of decomposition. 7

There are many advantages in the use of metals in place of non-metals for a formamide vaporizer. With metal construction, a smaller temperature' gradient between the vaporizing surface and heat source is possible, which greatly facilitates temperature control, prevents local overheating and decreases heat losses by radiation. Other advantageous properties possessed by metals are strength, resistance to sudden temperature changes and mechanical shocks, and ease and cheapness of fabrication.

The drawing shows one form of apparatus in which this invention may be carried out. The cylindrical metal vaporizing chamber (1) is provided with a metal inlet tube (2) and a relatively larger metal vapor outlet tube (5) the metal side tube (6) is connected at right angles to (5) a short distance above the vaporizing chamber (1) A thermometer (4), is suspended in tube (5), with its bulb just below the opening of tube (6). The inlet tube (2), is provided with a cooling jacket (3). The vaporizing chamber is immersed in the bath of molten metal (7) which is heated by the gas burner (8). It is to be understood that any common means of heating the vaporizer may be employed and that the combination of (7) and (8) as a heating means is disclosed solely as an example of one method.

In operation the vaporizing chamber (1) is heated by any suitable means, for instance by the molten metal bath ('7) and the liquid formamide is allowed to flow through the inlet tube (2) into the vaporizer. Cold water may be circulated through the jacket (3) to keep the infiowing formamide at approximately room temperature. The vaporized formamide is forced out of the vaporizingchamber by way of tubes (5) and (6) by the pressure resulting from its own accumulation and is led directly into the apparatus in which it is to be used. The heating of the vapori i g chamber and the rate of flow through the inlet are so regulated as to produce a formamide vapor having a temperature of between 200 C. and 300 C. and preferably below 260 C., at the outlet of the vaporizing chamber. Furthermore,

5 the flow of liquid formamide and the temperature of the vaporizing chamber are so regulated that substantially no liquid formamide accumulates on the bottom of the vaporizing chamber. The maximum rate of flow of liquid formamide then depends upon the rate at which heatis supplied to the heated surface. For a given temperature of the vaporizing surface, the greater the rate of feed without substantial accumulation of liquid on the vaporizing surface,

the less is the percentage of decomposition. Satisfactory results may be obtained by heating the exterior of the vaporizing chamber to a temperature even greater than 300 C., for instance to 370 (3., providing the rate of feed is high enough to maintain the temperature of the out-going vapor below 300 C. and preferably below 260 (3., as illustrated by the examples given below.

The following examples show the results obtained by this invention: 7

Example 1 A copper vaporizer was constructed substantially as described above. The vaporizing chamber 1) was a cylinder one inch high and 2 inches in diameter, inside dimensions. The inside diameters of the inlet tube (2) and outlet tube (5) were /4 inch and inch respectively. The side tube (6) was inch inside diameter and was 3 connected to tube (5) at a distance of 27 inches above the floor of the vaporizing chamber (1). Tube (6) was connected to a gas analysis apparatus, by means of which the amount of carbon monoxide and ammonia formed could be meas- The vaporizing chamber was heated by partial immersion in a molten metal bath, (7) which was in turn heated by the burner (8), and liquid formamide was introduced at various rates. The

per cent of decomposition was determined by measuring the amount of CO formed.

The following results were obtained:

A steel vaporizer, whose construction and dimensions were substantially identical with the vaporizer of Example l'were similarly heated. The following results were obtained:

Rateof feed Temperaof liquid Bath temture of es- Percent Iormannde peratur caping decompo- V (cc. per (C.) vapor sition minute) (C.)

Example 3 Formamide was vaporized in an aluminum vaporizer constructed similarly to that used in Examples 1 and 2, but heated by an electrical resistance in an enclosed space below the vaporizing chamber. The approximate temperature of the vaporizing surface was measured by means of a thermometer inserted in a well out in the bottom of the vaporizing chamber on the side next "to the heating element. The temperature of the vapor was measured at the entrance to the outlet tube.

The following data were obtained:

' Rate of feed Tempera- Temperaof liquid ture of vature of es- Percent formamide porizing caping decompo- (gms. per surface vapor sition minute) (C.) (C.)

6. 22 259 225 0. 5a 6. 43 269 236 0.01- 6.95 299 267 0.92 5.26 303 27a 0. 94 4. 70 250 228 0.67 a 22 a it It is evident that many forms of vaporizers for formamide may be devised without departing from this invention. For instance, a plurality of inlet or' outlet tubes or both could be used and the vaporizing chamber might have any one of a variety of shapes, without changing the essential characteristics of the apparatus. The inlet tube or tubes may be designed to introduce the liquid formamide as drops, small streams or a spray. Cooling means for the inlet tube may be dispensed with providing the flow of liquid formamide isfast enough to prevent substantial pre-heating. The vaporizer may be made of various metals, for. instance brass, iron, steel, copper and aluminum, and this invention is not limited to the use of any particular kind of metal.

I claim:

1. The process of vaporizing formamide comprising continuously contacting liquid formamide with a metal surface maintained at a temperature above the boiling point of said liquid formamide at the pressure existing at said metal surface and continuously removing formamide vapor from said metal surface said liquid being contacted at such a rate that it is vaporized substantially instantaneously.

2. The process of vaporizing formamide comprising continuously contacting liquid formamide with a metal surface maintained at a temperature above the boiling point of said liquid formamide at the pressure existing at said metal surface, said liquid being contacted at such a rate that there is substantially no accumulation of liquid on said heated metal surface and continuously removing formamide vapors from said heated surface.

3. The process of vaporizing formamide com-. prising continuously contacting liquid formamide with a metal surface which is maintained at a temperature above the boiling point of formamide at substantially 1 atmosphere, said liquid being contacted at such a rate that there is substantially no accumulation of liquid on the said heated metal surface, and continuously removing formamide vapors from said heated surface.

4. The process of vaporizing formamide comprising continuously contacting liquid formamide with a metal surface which is maintained 130 at a temperature between 200 C. and 370 C., said liquid being contacted at such a rate that there is substantially no accumulation of liquid on the said heated metal surface and continuously removing formamide Vapors from said heated surface.

5. The process of vaporizing formamide comprising continuously contacting liquid formamide with a metal surface which is maintained at a temperature between 200 C. and 300 C., said liquid being contacted at such rate that there is substantially no accumulation of liquid on the said heated metal surface and continuously removing formamide vapors from said heated surface.

6. The process of vaporizing formamide comprising continuously contacting liquid formamide with a heated metal surface at such a rate that there is substantially no accumulation of liquid on the said heated surface, continuously removing formamide vapor from said heated surface and adjusting the rate of flow of the said liquid and the temperature of the said heated surface so that the vapor formed is not heated to above 300 C.

'7. The process of vaporizing formamide comprising continuously contacting liquid formamide with a heated metal surface at such a rate that there is substantially no accumulation of liquid on the said heated surface, continuously removing formamide vapor from said heated surface and adjusting the rate of flow of the said liquid and the temperature of the said heated surface so that the vapor formed is not heated to above 300 C.

8. The process of vaporizing formamide comprising continuously contacting liquid formamide with a heated aluminum surface at such a rate that there is substantially no accumulation of liquid on the said heated surface, continuously removing formamide vapor from said heated surface and adjusting the rate of flow of the said liquid and the temperature of the said heated surface so that the vapor formed is not heated to above 300 C.

9. A process for vaporizing formamide which comprises contacting liquid formamide in a finely distributed condition with a metal surface, heated to a temperature between 200 C. and 370 C., while avoiding accumulation of liquid formamide.

PAUL JOHNSON CARLISLE. 

